1. Field of the Invention
The present invention relates to an iSCSI apparatus and, more particularly, to load reduction on a communication controller of the apparatus.
2. Related Background of the Invention
Recently, iSCSI (internet Small Computer System Interface) technology has been standardized by the Internet Engineering Task Force (IETF). SCSI technology is widely used as a technology for connecting storages to hosts. The iSCSI technology is a technology in which the SCSI technology is applied to an IP network such as a LAN. The iSCSI technology allows storages to directly connect to an IP network. The iSCSI protocol is a TCP/IP-based protocol. The iSCSI protocol establishes and manages connections between IP-based storage devices such as disk arrays and hosts as well as clients.
In the iSCSI technology, SCSI commands are encapsulated within IP packets. The IP packets encapsulating the SCSI commands are sent out over a network. Therefore, a sender-side computer needs to encapsulate the SCSI commands within the IP packets. The encapsulation within the IP packets involves processing of dividing the SCSI commands and data into smaller data elements. On the other hand, a receiver-side computer needs to decapsulate the IP packets. The decapsulation of the IP packets involves processing of combining the divided data and the like. If there is an error in the received data, many processings are required at the sender-side computer as well as at the receiver-side computer, such as request for data retransmission, retransmission of data in response thereto, checking of the correctness of the retransmitted data.
In the iSCSI technology, loads on communication controllers at both the sender and receiver sides are thus increased, in comparison with conventional technologies such as the SCSI technology and Fiber Channel technology. In addition, signals generated due to broadcasting and the address resolution protocol (ARP) travel over the computer network, and therefore the sender and receiver sides also need to process these signals.
Since the communication controller is in general realized by software, a load on a CPU increases as the load of the communication control processing increases. In order to reduce the load on the CPU, there exists a chip, called a TOE (TCP/IP offload engine), exclusively executing TCP/IP processing. A network adapter and the like which include the TOEs are also proposed. Nevertheless, a further increase in the load on the CPU is inevitable because, in future, transmission rates on a network are improved, the number of connected devices is increased, and transmission signals are increased with the increase in the number of connected devices. Accordingly, there is concern about deterioration in performance of an iSCSI apparatus such as a storage, which may accompany an increase in load on a CPU.
A conventional iSCSI technique is shown in Japanese Patent Laid-Open No. 2002-318725.